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more validation

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Mark Pilgrim
2009-08-05 22:32:29 -07:00
parent 6b48cf96c3
commit 751f096d5c
1 changed files with 6 additions and 6 deletions
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advanced-iterators.html
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@@ -168,7 +168,7 @@ if __name__ == '__main__':
AssertionError</samp>
<a><samp class=p>>>> </samp><kbd class=pp>assert 2 + 2 == 5, "Only for very large values of 2"</kbd> <span class=u>&#x2462;</span></a>
<samp class=traceback>Traceback (most recent call last):
File "<stdin>", line 1, in &lt;module>
File "&lt;stdin>", line 1, in &lt;module>
AssertionError: Only for very large values of 2</samp></pre>
<ol>
<li>The <code>assert</code> statement is followed by any valid Python expression. In this case, the expression <code>1 + 1 == 2</code> evaluates to <code>True</code>, so the <code>assert</code> statement does nothing.
@@ -178,7 +178,7 @@ AssertionError: Only for very large values of 2</samp></pre>
<p>Therefore, this line of code:
<pre class='nd pp'><code>assert len(unique_characters) <= 10, 'Too many letters'</code></pre>
<pre class='nd pp'><code>assert len(unique_characters) &lt;= 10, 'Too many letters'</code></pre>
<p>&hellip;is equivalent to this:
@@ -250,7 +250,7 @@ gen = ord_map(unique_characters)</code></pre>
<samp class=pp>(3, 2)</samp>
<a><samp class=p>>>> </samp><kbd class=pp>next(perms)</kbd> <span class=u>&#x2464;</span></a>
<samp class=traceback>Traceback (most recent call last):
File "&lt;stdin>", line 1, in <module>
File "&lt;stdin>", line 1, in &lt;module>
StopIteration</samp></pre>
<ol>
<li>The <code>itertools</code> module has all kinds of fun stuff in it, including a <code>permutations()</code> function that does all the hard work of finding permutations.
@@ -279,7 +279,7 @@ StopIteration</samp></pre>
<samp class=pp>('C', 'B', 'A')</samp>
<samp class=p>>>> </samp><kbd class=pp>next(perms)</kbd>
<samp class=traceback>Traceback (most recent call last):
File "&lt;stdin>", line 1, in <module>
File "&lt;stdin>", line 1, in &lt;module>
StopIteration</samp>
<a><samp class=p>>>> </samp><kbd class=pp>list(itertools.permutations('ABC', 3))</kbd> <span class=u>&#x2462;</span></a>
<samp class=pp>[('A', 'B', 'C'), ('A', 'C', 'B'),
@@ -582,8 +582,8 @@ NameError: name '__import__' is not defined</samp>
<samp class=p>>>> </samp><kbd class=pp>eval("__import__('subprocess').getoutput('rm -rf /')",</kbd>
<a><samp class=p>... </samp><kbd class=pp> {"__builtins__":None}, {})</kbd> <span class=u>&#x2461;</span></a>
<samp class=traceback>Traceback (most recent call last):
File "&lt;stdin>", line 1, in <module>
File "&lt;string>", line 1, in <module>
File "&lt;stdin>", line 1, in &lt;module>
File "&lt;string>", line 1, in &lt;module>
NameError: name '__import__' is not defined</samp></pre>
<ol>
<li>To evaluate untrusted expressions safely, you need to define a global namespace dictionary that maps <code>"__builtins__"</code> to <code>None</code>, the Python null value. Internally, the &#8220;built-in&#8221; functions are contained within a pseudo-module called <code>"__builtins__"</code>. This pseudo-module (<i>i.e.</i> the set of built-in functions) is made available to evaluated expressions unless you explicitly override it.